Five small stable RNA species have been isolated from Mycoplasma capricolum. Together with the previously found RNA species, M.capricolum contains at least six small RNAs besides rRNAs and tRNAs. The sequences of these RNAs, designated MCS1 to MCS6, have been determined. MCS1 RNA is homologous to 4.5S RNA of E. coli, MCS5 to 10Sa RNA and MCS6 to M1 RNA (RNase P RNA). Unexpectedly, MCS4 RNA revealed an extensive sequence similarity to eukaryotic U6 snRNAs. MCS6, 10Sa RNA homolog, contains a tRNA-like structure in the 5'- and 3'-terminal sequences.